In conventional commercial aircraft wing design, it is common to use a structural box to carry the majority of the load developed by lift and other high load devices. An example of part of such a structural box 1 is illustrated in the perspective view of FIG. 1 from which it can be seen that it is built from a number of different sections including spars 2, ribs 3 and stringers 4, which form the main load-bearing structural components of the wing, with a lower wing cover 5 and an upper wing cover(not shown) forming an outer skin surface.
The stringers 4 are attached to the inside of the wing covers 5 and provide support. The ribs 3 extend transversely to the stringers 4 to shape the cross-sectional profile of the aircraft wing and provide additional support to the wing covers 5. The space inside the structural box 1 may form a fuel tank (not shown), with the wing covers 5 enclosing the fuel tank. The ribs 3 are secured to the stringers 4 to prevent the ribs 3 from moving relative to the wing covers 5 and to hold the covers 5 is position such that they are not deformed by the pressure exerted thereon by the fuel in the fuel tank.
In conventional wing structures, the ribs 3 are secured to the stringers 4 and covers 5 using a plurality of brackets (not shown) that are bolted to the ribs 3 and through the covers 5. A hole is drilled in the body of each of the stringers 4 such that the bracket can be bolted thereon to secure the rib 3 relative to the stringer 4. However, it has been found that drilling a hole in the body of the stringer 4 reduces the strength and stiffness of the stringer 4. In addition, the bolt heads protrude from the outside surfaces of the covers 5 such that the aerodynamic drag of the covers 5 is increased. Furthermore, if bolt holes are drilled through the portion of the covers 5 that form the fuel tank, the bolt holes will need to be carefully sealed to prevent fuel leaking through the bolt holes. Such sea s increase the manufacturing complexity of the wing structure.
Each of the brackets must be manufactured to extremely tight tolerances to ensure that when the brackets are mounted to the stringers 4, each of the ribs 3, stringers 4 and covers 5 are correctly aligned so that the cross-sectional profile of the aircraft wing is not distorted. Alternatively, differences in the profile of the bracket and the stringer 4 may be rectified by shimming. However, shimming makes high volume and/or low cost manufacture of the structural box difficult. Furthermore, the stringer 4 must be provided with a portion of increased width to provide sufficient surface area for the bracket to be bolted to. However, this portion of increased width adds weight to the stringer 4. In some configurations the brackets are bonded to the stringer 4. However, such a configuration may still require that the bracket is additionally bolted to the stringer 4 for fail safe reasons in the event that the bond fails.
The present invention seeks to overcome or substantially alleviate at least some of the problems with conventional assemblies referred to above.